Concrete and Stone Materials
Humans have known and used concrete and stone since ancient times. For example, materials such as concrete, slate, granite and marble are used in constructing various useful structures.
Concrete has been used for all manner of structures, including roads, buildings and building components such as pipe, block, pavers, and railroad ties. Concrete has many beneficial properties such as being hard (or resistant to deformation by mechanical forces), fireproof, water repellent, and resistant to the elements including resistance to mold growth and fungus growth.
Slate is a fine grained, metamorphic rock composed primarily of quartz and mica (sometimes formulated as KAl2(AlSi3O10)). Because slate is planar, hard, fireproof, water repellent, and resistant to the elements including resistance to mold growth and fungus growth, it finds broad uses in building and construction, such as paver and roofing materials. Slate occurs in a variety of colors, for example, grey (pale to dark), green, cyan (bluish-green) or purple colors. Slate is generally “foliated”, or layered, such that it cleaves to give distinctive, planar surface patterns. Its unique aesthetic and physical qualities have made slate a desirable material in building and construction as well as in decorative art and sculpture.
Artificial slate-like materials have been studied in efforts to replace the more expensive and scarce natural slate with low-cost, readily produced mimics. Such efforts, however, have yet to produce in a synthetic material that possesses the desired appearance, texture, density, hardness, porosity and other aesthetics characteristic of slate while at the same can be manufactured in large quantities at low cost with minimal environmental impact.
“Composite slate” is s simulated slate replacement made from recycled rubber and plastic. While these products resemble slate in appearance and in some properties (primarily that they are water repellent and resist the elements), they lack slate's hardness, they are not fireproof to the extent that slate is fireproof, and they have a distinctly different “feel”. Up close, they look different. Finally, although they may contain recycled materials, they are based on materials derived from petrochemical products.
Laminated asphalt sheets have the artificial look that has made them considerably less desirable than the natural slate. Other artificial slate mimics are prepared with a synthetic resin binder. These methods suffer from a number of deficiencies, including poor reproducibility, low yield, deterioration, high finishing costs, unsatisfactory mechanical properties, and the like.
Granite is an igneous rock comprising principally quartz, mica and feldspar. It usually has coarse grains within a fine-grained matrix. It is known to occur in nature with various coloration.
Humans have known and used granite since ancient times. Its unique aesthetic and physical qualities have made granite a desirable material in building and construction as well as in decorative art and sculpture. Artificial granite-like materials have been studied in efforts to replace the expensive and scarce material with low-cost, readily produced mimics. Such efforts, however, have yet to produce in a synthetic material that possesses the desired appearance, texture, density, hardness, porosity and other aesthetics characteristic of granite while at the same can be manufactured in large quantities at low cost with minimal environmental impact.
Most artificial granite mimics are prepared by blending natural stone powder and minerals with a synthetic resin (e.g., acrylic, unsaturated polyester, epoxy). These methods suffer from a number of deficiencies, including poor reproducibility, low yield, deterioration, high finishing costs, unsatisfactory mechanical properties, and the like.
Humans have known and used marble since ancient times. Its unique aesthetic and physical qualities have made marble a desirable material in building and construction as well as in decorative art and sculpture. Artificial marble-like materials have been studied in efforts to replace the expensive and scarce material with low-cost, readily produced mimics. Such efforts, however, have yet to produce in a synthetic material that possesses the desired appearance, texture, density, hardness, porosity and other aesthetics characteristic of marble while at the same can be manufactured in large quantities at low cost with minimal environmental impact.
Most artificial marble mimics are prepared by blending natural stone powder and minerals with a synthetic resin (e.g., acrylic, unsaturated polyester, epoxy). These methods suffer from a number of deficiencies, including poor reproducibility, low yield, high finishing costs, deterioration, unsatisfactory mechanical properties, and the like.
Conventional Concrete Curing Chambers
Traditional concrete curing chambers are employed in a variety of precast concrete industries. A curing chamber is a fully or partially enclosed volume within which a controlled environment can be created. The enclosed volume may defined by the solid walls of a rigid structure such as a room or by a flexible barrier such as a tarp in the form of a tent. After a concrete specimen is formed, it is placed in a controlled environment with sufficient moisture content and high enough temperature to ensure that adequate curing is reached in reasonable times, typically measured in days. Curing is vital to the quality of the concrete products and has a strong influence on properties such as durability, strength and abrasion resistance. Proper curing also aids to mitigate secondary reactions that occur over time that may cause defects and unwanted color changes of the finished products.
Curing of concrete aids the chemical reaction of Portland cement concrete known as hydration. The chamber is intended to keep the controlled environment conditioned and to maintain proper moisture within the product for the duration of the curing process. Any appreciable loss of moisture will significantly delay or prevent hydration and therefore decrease the properties of the product. Also, temperature plays a critical role during the curing process as temperatures below 10 C or above 70 C are highly unfavorable for curing while a temperature of 60 C is optimum.
Some companies that produce precast concrete attempt simplified curing processes using large rooms or areas covered by tarps which house the products in an attempt to maintain temperature and humidity. These systems may act as a means to retain heat generated from the samples as a result of the exothermic reaction that occurs during the hydration reaction or to retain heat or humidity that may be provided by external heaters or water spraying systems. The most efficient and effective method to cure precast concretes, however, relies on a permanent, sealed and controllable curing environment.
Several companies exist that specialize in the design, manufacturing, and installation of Portland cement concrete curing chambers for the precast industry in the production of a wide range of products included but not limited to paving stones, concrete masonry units (CMU's), retaining walls, and roofing tiles. These curing systems are most often constructed of steel, typically galvanized steel, and are insulated to prevent heat loss and maintain energy efficiency. Some systems are highly automated and include “finger cars” which are automated transfer systems that take the formed precast products from the former into the curing chamber racks. Commercial curing systems can range from the size of a standard shipping container (approximately 40 ft×10 ft×8 ft) all the way up to high volume production systems that could be as large as 200 ft×100 ft×50 ft. The chambers can be configured as one “Big Room” system if the product is consistent, but for manufacturers with many products lines a “Multi Lane” system is usually employed that allows for separate temperature and humidity profile control of each individual bay that may be home to a different product line.
FIG. 1 is a schematic diagram of a traditional (prior art) concrete curing chamber, including the primary components which are a circulation system, a heat exchanger, and a humidification system. The system may contain one or many blowers for gas circulation that provide high enough gas velocities across the products to allow for distribution of temperature and humidity as required. The heat exchanger can employ a direct gas fired burner, an indirect gas fired burner, or an electric heater. The humidification system usually includes atomizing spray nozzles or a heated vapor generator to provide water vapor to the system. Both temperature and humidity are monitored by sensors that send signals back to a computer or programmable logic controller that is used to control the curing parameters. Many systems allow for complete sequenced automation with temperature and humidity ramp up, dwell, and cool down steps such as are shown in FIG. 2 FIG. 2 is a graph that illustrates a traditional (prior art) concrete curing profile showing temperature as a function of time.
Treatment Systems Using Carbon Dioxide
Among the descriptions of systems that use carbon dioxide as a reactant are:
Kraft Energy, which describes their use in a number of documents such as Kraft Energy Concrete Curing Systems. Kraft Energy at page 195 states that carbonation (of concrete) is “[a] process by which carbon dioxide from the air penetrates the concrete and reacts with the hydroxides, such as calcium hydroxide, to form carbonates. In the reaction with calcium hydroxide, calcium carbonate is formed.” At page 37, Kraft Energy shows an illustration of a paver stone that has been carbonated. The caption under the image states “Typical carbonation found after vapor curing a 7 N/mm2 solid block for 24 hours. (Phenolphthalein indication).” The image shows a rectangular block that has a grey region on its surfaces, and a purple center region. It is known that phenolphthalein is a chemical compound with the formula C20H14O4. It turns colorless in acidic solutions and pink in basic solutions. If the concentration of indicator is particularly strong, it can appear purple. As is evident from the image, the carbonation only proceeds to a shallow depth and does not occur in the central portion of the block.
Also known in the prior art is Murray, U.S. Pat. No. 4,117,060, issued Sep. 26, 1978, which is said to disclose a method and apparatus is provided for the manufacture of products of concrete or like construction, in which a mixture of calcareous cementitious binder substance, such as cement, an aggregate, a vinyl acetatedibutyl maleate copolymer, and an amount of water sufficient to make a relatively dry mix is compressed into the desired configuration in a mold, and with the mixture being exposed to carbon dioxide gas in the mold, prior to the compression taking place, such that the carbon dioxide gas reacts with the ingredients to provide a hardened product in an accelerated state of cure having excellent physical properties.
Also known in the prior art is Malinowski, U.S. Pat. No. 4,362,679, issued Dec. 7, 1982, which is said to disclose a method of casting different types of concrete products without the need of using a curing chamber or an autoclave the concrete subsequent to mixing, is casted and externally and/or internally subjected to a vacuum treatment to have it de-watered and compacted. Then carbon-dioxide gas is supplied to the mass while maintaining a sub- or under-pressure in a manner such that the gas-as a result of the sub-pressure-diffuses into the capillaries formed in the concrete mass, to quickly harden the mass. In one embodiment (cf. FIG. 2)—in which the mass (I) is de-watered and compacted by means of a mat or plate (2) placed thereupon and exposed to a sub-pressure via a pipe or a line (5)—the carbon-dioxide gas is supplied (through line 6) via said mat or plate (2) while using the under-pressure prevailing in the mass. In another embodiment (cf. FIG. 3) the sub-pressure is applied (via line 5) from one or more sides (2b) of the mould to the interior of the element being cast, either by means of special inserts, by holes or cavities inside the element or via a porous material layer (I b) in the inner portion thereof. Then the carbon-dioxide gas is supplied correspondingly (via line 6). These two main embodiments may in certain cases be combined in different ways. Further the concrete may at the same time or subsequently be subjected to another type of treatment such as impregnation by a suitable solution.
Also known in the prior art is Getson, U.S. Pat. No. 4,862,827, issued Sep. 5, 1989, which is said to disclose at column 3, lines 26-32, that “Referring to FIG. 1, there is shown air intake 33 and exhaust 37, with chamber 35 downstream of the air path from air intake 33. This chamber may be used for introducing carbon dioxide for accelerating and curing certain compositions and/or it may be used for introducing 30 additional moisture to further accelerate curing of moisture-curable systems.”
Also known in the prior art is Charlebois, U.S. Pat. No. 5,800,752, issued Sep. 1, 1998, which is said to disclose polymer composite products, including products made of polymer concrete, reinforced polymer concrete and reinforced plastics, such as bulk: molding compound, sheet molding compound, mineral molding compound and advanced molding compound systems, are produced by the simultaneous application of vibration, heat and pressure to a mixture of filler and polymeric binder. The simultaneous application of vibration, heat and pressure provides a protective layer of polymerized binder that protects the surfaces of the mold and provides products that are substantially free of curling, cracking or voids. The process of the present invention substantially reduces the time required to cure polymer composite products.
Also known in the prior art is Soroushian et al., U.S. Pat. No. 5,935,317, issued Aug. 10, 1999, which is said to disclose a CO2 pre-curing period is used prior to accelerated (steam or high-pressure steam) curing of cement and concrete products in order to: (1) prepare the products to withstand the high temperature and vapor pressure in the accelerated curing environment without microcracking and damage; and (2) incorporate the advantages of carbonation reactions in terms of dimensional stability, chemical stability, increased strength and hardness, and improved abrasion resistance into cement and concrete products without substantially modifying the conventional procedures of accelerated curing. Depending on the moisture content of the product, the invention may accomplish CO2 pre-curing by first drying the product (e.g. at slightly elevated temperature) and then expose it to a carbon dioxide-rich environment. Vigorous reactions of cement paste in the presence of carbon dioxide provide the products with enhanced strength, integrity and chemical and dimensional stability in a relatively short time period. Subsequent accelerated curing, even at reduced time periods (with less energy and cost consumptions) would produce higher performance characteristics than achievable with the conventional pre-setting period followed by accelerated curing of cement and concrete products.
Also known in the prior art is Ramme et al., U.S. Pat. No. 7,390,444, issued Jun. 24, 2008, which is said to disclose a process for sequestering carbon dioxide from the flue gas emitted from a combustion chamber is disclosed. In the process, a foam including a foaming agent and the flue gas is formed, and the foam is added to a mixture including a cementitious material (e.g., fly ash) and water to form a foamed mixture. Thereafter, the foamed mixture is allowed to set, preferably to a controlled low-strength material having a compressive strength of 1200 psi or less. The carbon dioxide in the flue gas and waste heat reacts with hydration products in the controlled low-strength material to increase strength. In this process, the carbon dioxide is sequestered. The CLSM can be crushed or pelletized to form a lightweight aggregate with properties similar to the naturally occurring mineral, pumice.
Also known in the prior art is CARBONCURE TECHNOLOGIES INC., International Patent Application Publication No. WO 2012/079173 A1, published 21 Jun. 2012, which is said to disclose concrete articles, including blocks, substantially planar products (such as pavers) and hollow products (such as hollow pipes), are formed in a mold while carbon dioxide is injected into the concrete in the mold, through perforations.
All of the above documents that describe reactions of carbon dioxide with concrete are dealing with concrete that has Portland cement as a binding agent. Portland cement cures in the absence of CO2 via a hydration reaction.
Furthermore, existing methods typically involve large energy consumption and carbon dioxide emission with unfavorable carbon footprint.
There is an on-going need for an apparatus and methods for fabricating novel composite materials that exhibit useful aesthetic and physical characteristics and can be mass-produced at low cost with improved energy consumption and desirable carbon footprint.